Scouring method

ABSTRACT

A method and apparatus for removing fouling materials from the surface of a plurality of porous membranes ( 9 ) arranged in a membrane module ( 4 ) by providing, from within the module, by means ( 10 ) other than gas passing through the pores of said membranes, gas bubbles in a uniform distribution relative to the porous membrane array such that the bubbles move past the surfaces of the membranes ( 9 ) to dislodge fouling materials therefrom. The membranes ( 9 ) are arranged in close proximity to one another and mounted to prevent excessive movement therebetween. The bubbles also produce vibration and rubbing together of the membranes to further assist removal of fouling materials.

RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.10/369,813, filed Feb. 18, 2003, which is a continuation of applicationSer. No. 09/336,059, filed Jun. 18, 1999, which is a continuation, under35 U.S.C. § 120, of International Patent Application No. PCT/AU97/00855,filed on Dec. 18, 1997 under the Patent Cooperation Treaty (PCT), whichwas published by the International Bureau in English on Jul. 2, 1998,which designates the U.S. and claims the benefit of AustralianProvisional Patent Application No. PO 4312, filed Dec. 20, 1996 andAustralian Provisional Patent Application No. PO 8918, filed Sep. 1,1997.

FIELD OF THE INVENTION

[0002] The present invention relates to the use of a gas bubble systemto remove fouling materials from the surface of membranes used infiltration systems and the like.

BACKGROUND OF THE INVENTION

[0003] A variety of membrane filtration systems are known and many ofthese use pressurised systems operating at high transmembrane pressures(TMP) to produce effective filtering and high filtrate flux. Thesesystems are highly effective but are also expensive to produce, operateand maintain. Simpler systems using membrane arrays freely mountedvertically in a tank and using suction applied to the fibre lumens toproduce TMP have also been developed, however, these systems have beenfound in the past to be less effective than the pressurised systems.

[0004] Examples of such known systems are illustrated in U.S. Pat. No.5,192,456 to Ishida et al, U.S. Pat. No. 5,248,424 to Cote et al and WO97/06880 to Zenon Environmental Inc.

[0005] The Ishida et al patent describes an activated sludge treatingapparatus where air flow is used to clean the outer surface of thefilter membrane. In this arrangement the air blower used for biologicaltreatment of the waste water is also used as a secondary agitationsource to clean the surface of the membranes. The membrane modules areof the plate type. The membranes also have a low packing density andthus do not have the problems associated with cleaning tightly packedfibre bundles. Air is bubbled from beneath the modules and is suppliedexternally from the membrane array.

[0006] The Cote et al patent again describes a system of cleaning arraysof fibres. In this case the fibres are mounted in a skein to form aninverted U-shaped or parabolic array and the air is introduced below thearray to produce bubbles which contact the fibres with such force theykeep the surfaces relatively free of attached microorganisms anddeposits of inanimate particles. The fibres are freely swayable as theyare only attached at either end and this assists removal of deposits ontheir outer surface. The bubbles of gas/air flow are provided from asource external of the fibre bundle and move generally transverse to thelengths of fibre. This limits the depth of fibre bundle which can beeffectively cleaned.

[0007] The invention disclosed in the Zenon Environmental, Inc. PCTApplication No. WO 97/06880 is closely related to the Cote et al patent.In this document the fibres are unconfined, vertically arranged anddimensioned to be slightly longer than the distance between the opposedfaces of the headers into which the fibre ends are mounted to allow forswaying and independent movement of the individual fibres. The skein isaerated with a gas distribution means which produces a mass of bubbleswhich serve to scrub the outer surface of the vertically arranged fibresas they rise upwardly through the skein.

[0008] Our own International Patent Application WO96/07470 describes anearlier method of cleaning membranes using a gas backwash to dislodgematerial from the membrane walls by applying a gas pressure to thefiltrate side of the membranes and then rapidly decompressing the shellsurrounding the feed side of the membranes. Feed is supplied to theshell while this gas backwash is taking place to cause turbulence andfrothing around the membrane walls resulting in further dislodgment ofaccumulated solids.

SUMMARY OF THE INVENTION

[0009] The present invention relates particularly to a plurality ofporous membranes arranged to form a membrane module arranged in arelatively tightly packed bundle. These porous membranes may be in theform of fibres or plate type membranes as described in the above priorart.

[0010] The present invention seeks to overcome or at least amelioratethe problems of the prior art by providing a simple effective system andmethod for removing fouling materials from the surface of the porousmembranes by use of gas bubbles.

[0011] According to one aspect, the present invention provides a methodof removing fouling materials from the surface of a plurality of porousmembranes arranged in a membrane module, the porous membranes forming anarray, the module having a header used to mount the membranes, theheader connected to a source of pressurized gas, the method comprisingproviding, through the header, gas bubbles in a uniform distributionrelative to the porous membrane array such that said bubbles move pastthe surfaces of said membranes to dislodge fouling materials therefrom,said membranes being arranged in close proximity to one another andmounted to prevent excessive movement therebetween. The porous membranesmay comprise hollow fibre membranes. Preferably, the fibre membranes arearranged in bundles surrounded by a perforated cage which serves toprevent said excessive movement therebetween.

[0012] According to a second aspect, the present invention provides amembrane module comprising a plurality of porous membranes, saidmembranes being arranged in close proximity to one another and mountedto prevent excessive movement therebetween, the membranes forming anarray, the module having a header used to mount the membranes, theheader connected to a source of pressurized gas so as to permitformation of gas bubbles such that, in use, said gas moves through saidheader, and said bubbles move past the surfaces of said membranes todislodge fouling materials therefrom.

[0013] The gas bubbles may be provided from within the module by avariety of methods including gas distribution holes or openings in theheader, a porous tube located within the module or a tube or tubespositioned to output gas within the module, the tubes may be in the formof a comb of tubes containing holes which sit within the module. Anothermethod of providing gas bubbles includes creating gas in-situ by meansof spark type ozone generators or the like. Further types of gasprovision are detailed below and in the preferred embodiments of theinvention.

[0014] According to one preferred form, the present invention provides amethod of removing fouling materials from the surface of a plurality ofporous hollow fibre membranes mounted and extending longitudinally in anarray to form a membrane module, said membranes being arranged in closeproximity to one another and mounted to prevent excessive movementtherebetween, the method comprising the steps of providing, from withinsaid array, via the header connected to a source of pressurized gas,uniformly distributed gas bubbles, said distribution being such thatsaid bubbles pass substantially uniformly between each membrane in saidarray to scour the surface of said membranes and remove accumulatedsolids from within the membrane module.

[0015] For preference, said membranes are mounted vertically to formsaid array and said bubbles pass generally parallel to the longitudinalextent of said fibres. Preferably, said uniformly distributed gasbubbles are provided at the lower end of the array. Optionally, abackwash may be used in conjunction with the removal process to assistsolids removal from the membrane pores and outer surface of themembranes.

[0016] For preference, the membranes comprise porous hollow fibres, thefibres being fixed at each end in a header, the lower header having aplurality of holes formed therein through which gas is introduced toprovide the gas bubbles. The fibres are normally sealed at the lower endand open at their upper end to allow removal of filtrate. Some of thefibres may also be used to provide bubbles of scouring gas to the arrayby feeding gas through selected ones of the fibres in the array. Thefibres are preferably arranged in cylindrical arrays or bundles.

[0017] Filtrate is normally withdrawn from the fibres by application ofsuction applied thereto, however, it will be appreciated that anysuitable means of providing TMP may be used. A porous sheet may be usedin conjunction with the holes or separately to provide a more uniformdistribution of gas bubbles. The porous sheet also provides the addedadvantage of preventing solids ingressing into the air supply plenumchamber.

[0018] According to a further preferred aspect, the present inventionprovides a membrane module comprising a plurality of porous hollowmembrane fibres extending longitudinally between and mounted at each endto a respective potting head, said membrane fibres being arranged inclose proximity to one another and mounted to prevent excessive movementtherebetween, one of said potting heads having a uniform distributedarray of aeration holes formed therein and said fibres beingsubstantially uniformly mounted in said one potting head relative tosaid aeration holes.

[0019] According to a preferred further aspect, the present inventionprovides a filtration system including a membrane module according tosaid second aspect wherein said filter module is positioned verticallyin a tank containing feed liquid to be filtered, means to apply atransmembrane pressure to said fibres in said array to cause filtrate topass through pores in said fibres and means to supply continually orintermittently a supply of pressurized gas to said aeration holes so asto produce gas bubbles which move upwardly and uniformly between saidfibres to scour the outer surfaces thereof.

[0020] Optionally, when the module is contained in a separate vessel,periodic draindown of the vessel is carried out after the scouring stepto remove solids accumulated during the scouring process. Apart fromdraindown, other methods can be used for accumulated solids removal.These include continual bleed off of concentrated feed during thefiltration cycle or overflow at the top of the tank by pumping feed intothe base of the tank at regular intervals at a rate sufficient to causeoverflow and removal of accumulated solids. This would be typically doneat the end of a backwash cycle.

[0021] It should be understood that the term “gas” used herein includesany gas, including air and mixtures of gases as well as ozone and thelike.

[0022] It will be appreciated that the above described invention may bereadily applied to our own modular microporous filter cartridges as usedin our continuous microfiltration systems and described in our earlierU.S. Pat. No. 5,405,528. These cartridges may be modified by providinggas distribution holes in the lower plug and providing a manifold forsupplying gas to said holes such that, in use, the gas passes throughthe holes and forms scouring bubbles which pass upward through thefilter medium. In a preferred arrangement, the filter medium would besealed at the lower end and filtrate withdrawn under a vacuum from theupper end while the cartridge or cartridges were positioned in a tankcontaining the feed.

[0023] The embodiments of the invention will be described in relation tomicroporous fibre membranes, however, it will be appreciated that theinvention is equally applicable to any form of membrane module.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Preferred embodiments of the present invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

[0025]FIG. 1 shows a simplified cross-sectional view of one embodimentof a membrane module in accordance with the present invention;

[0026]FIG. 2 shows a simplified two part representation of the pottingarrangement of the membrane module according to one preferred form ofthe invention;

[0027]FIG. 3 shows an enlarged view of the potting base of FIG. 2;

[0028]FIGS. 4A and 4B show the pin formations in the annular portion ofthe potting base and the plunger portion of the potting base,respectively;

[0029]FIG. 5 shows schematic diagram of a filtration system using themembrane module of FIG. 1;

[0030]FIG. 6 shows a simplified cross-sectional view of an alternateembodiment of the membrane module according to the present invention;

[0031]FIG. 7 shows a simplified cross-sectional view of an alternateembodiment in terms of feeding of air to the membrane module of thepresent invention;

[0032]FIGS. 8A and 8B shows two graphs illustrating the suctionperformance of the module under different conditions;

[0033]FIG. 9 shows a graph of resistance increase over time with 30minute suction stage;

[0034]FIG. 10 shows a graph of resistance increase over time betweenbackwashes without a porous sheet;

[0035]FIG. 11 shows a graph of resistance increase over time betweenbackwashes with the porous sheet;

[0036]FIG. 12 shows a graph of resistance changes over time with gasbubble scouring at regular intervals but no liquid backwash of the fibremembranes;

[0037]FIG. 13 shows a similar graph to FIG. 12 illustrating the effectof no bubble scouring on backwash efficiency; and

[0038]FIG. 14 shows a similar graph to FIG. 12 illustrating the effectof applying gas bubble scouring to the outer side of the fibre bundleonly.

[0039]FIGS. 15a-c show a comb of tubes containing holes, the tubesitting within a module and providing pressurized gas bubbles.

[0040]FIG. 16 shows a module incorporating a porous sheet through whichpressurized gas is supplied to provide gas bubbles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0041] Referring to FIG. 1, the membrane module 4, according to thisembodiment, comprises a cylindrical array or bundle of hollow fibremembranes 5 extending longitudinally between upper and lower pottingheads 6, 7. Optionally, a screen or cage 8 surrounds the array 5 andserves to hold the fibres 9 in close proximity to each other and preventexcessive movement. The fibres 9 are open at the upper potting head 6 toallow for filtrate removal from their lumens and sealed at the lowerpotting head 7. The lower potting head 7 has a number of holes 10uniformly distributed therein to enable gas/air to be suppliedtherethrough. The fibres are fixed uniformly within the potting heads 6and 7 and the holes 10 are formed uniformly relative to each fibre 9 soas to provide, in use, a uniform distribution of gas bubbles between thefibres.

[0042] The holes are formed as part of the potting process as describedbelow. The arrangement of the holes relative to one another as well asthe arrangement of fibres relative to the holes and each other has beenfound to effect the scouring efficiency of the gas bubbles.

[0043] The maldistribution of gas within the fibre bundle can beovercome by appropriate distribution and sizing of holes to ensure thatbubble flow around the fibres is uniform across the bundle. In acylindrical bundle of closely packed fibres it has been found that thedistance traveled through the bundle by bubbles introduced towards thecentre of the bundle is larger than those introduced towards the outerextremity of the bundle, resulting in a higher resistance to bubble flowat the centre of the bundle than at its border or periphery.

[0044] As outlined above, one method of addressing the maldistributionof gas bubbles is to provide a porous sheet (not shown) across the holesto provide an even pore distribution and thus a uniform gas flow.Another method is to provide a distribution of hole size relative to thedistribution of resistance. Since the gas flowrate (Q) per unit area (A)is inversely proportional to the resistance (R),

[0045] Q/A˜1/R the relationship between the hole diameter (d) and theresistance becomes

[0046] d˜(R)^(1/2) using the above relationship it is possible to designa hole size and position configuration which compensates for resistancedifferences within the bundle. For example, if the resistance at thecentre of the bundle is 50% higher than that at its periphery, the holesize at the centre (d_(c)) and on the periphery (d_(p))would be thefollowing for a uniform distribution of gas:

[0047] d_(c)/d_(p)=1.5^(0.5)=1.22

[0048] Known methods of forming holes require the drilling of holes orother forms of post-potting formation. Such methods have thedisadvantage of requiring avoidance of the fibres/membranes whendrilling or the like to avoid damage. This imposes limitations on thefibre packing density and hole size as, where fibres are tightly packed,it very difficult to drill holes without interfering with or damagingthe fibres. Further, it is difficult to accurately locate holes relativeto the fibres/membranes.

[0049] The process used in one aspect of the present invention seeks toovercome or at least the ameliorate the problems and disadvantagesoutlined above.

[0050] According to this aspect, the present invention provides a methodof forming openings in a membrane pot for use in gas distributioncomprising the steps of: providing a mould for potting membrane ends,said mould having provided therein formations for forming said openingsduring the potting process; positioning said membrane ends in said mouldwhich is filled with a curable potting material; allowing said pottingmaterial to at least partially cure and, demoulding said membranes.

[0051] Preferably, said membranes ends are uniformly distributed inrelation to said formations. In another aspect, the invention includes amembrane assembly including at least one membrane pot formed accordingto the above method.

[0052] Referring to FIGS. 2-4, the preferred method of forming the gasdistribution holes will be described. As shown in the right side part ofFIG. 2, the potting apparatus (shown empty) comprises a potting mould 20mounted on a vertically movable platform 21 which is raised and loweredby means of hydraulic cylinder 22. The centre of each mould 20 isprovided with a vertically movable ejector plunger 23 operated by andhydraulic ejector cylinder 24. A fibre guide or collar 25 fits aroundthe periphery of the mould to guide and hold the fibre ends during thepotting process as well as retaining the potting mixture, typicallypolyurethane, within the mould. The fibres are held within a sleeve 26when inserted into the guide 25. The base 20′ of the mould 20 has aplurality of upstanding pins 27 which serve the dual purpose ofassisting even distribution of the fibre ends and forming the gasdistribution holes in the pot. The pins are sized and distributed asrequired for correct gas bubble distribution. One form of pindistribution is shown in FIG. 4.

[0053] In use, the guide 25 is placed about the mould 20 and the mould20 filled to the required level with potting material. The platform 21is then raised to lower the fibre ends into the mould 20. The fibre endsare normally fanned before insertion to ensure even distribution andalso trimmed to ensure a uniform length.

[0054] Once the potting material has partially cured, the pot is ejectedfrom the mould by raising the central ejector portion 23 of the mould.The mould 20 is normally heated to assist curing. If desired, the mould20 may be centrifuged during the potting process to assist thepenetration of the potting material into the fibre walls.

[0055] This process normally results in the ends of the fibres in thispot being sealed, however, it will be appreciated that, by appropriatetransverse cutting of the pot, the fibre ends may be opened forwithdrawal of filtrate from the lumens.

[0056] A trial module 4 of this type was packed with 11,000 fibres(o.d./i.d. 650/380 μm). The fibre lumens at the lower end were blockedwith polyurethane and 60 holes of 4.5 mm in diameter distributed withinthe fibre bundle. The lower end was connected to an air line sealed fromthe feed.

[0057]FIG. 5 illustrates the setup of the trial unit. The module 4 wasarranged vertically in the cylinder tank 15 and the filtrate withdrawnfrom the top potting head 6 through suction. Air was introduced into thebottom of the module 4, producing air bubbles between fibres to scrubsolids accumulated on membrane surfaces. To remove solids clogged withinmembrane pores, a small quantity of permeate was pumped through fibrelumens (permeate backwash). One method of operation was to run suctionfor 15 minutes, then aeration for 2 minutes 15 seconds. After a firstminute of aeration, a permeate backwash is introduced for 15 seconds.The cycle returns to suction. After several cycles, the solids in thecylinder tank 15 were concentrated and the water in the tank 15 wasdrained down to remove concentrated backwash.

[0058] In the preferred embodiment shown in FIG. 1, gas/air should beuniformly distributed and flow through the small holes 10 at the lowerend of the module 4 so that air bubbles can be produced between fibres9. Air bubbles then flow upwards producing shear force to scour solidsaccumulated on the membrane surfaces. If the resistance around the holes10 is variable due to varying resistance provided by different regionsof the fibre bundle, gas/air will tend to flow through those holesassociated with a lower resistance, resulting in by-pass flow throughthese holes.

[0059] In the manufacture of membrane modules 4, it is desirable to potthe fibres 9 in a uniform distribution relative to the holes 10.Moreover, smaller and more holes will help distribution of gas/air, butholes that are too small will reduce bubble size and thus the shearforce applied to the outer surface of the fibres. It is preferable thatsize of holes should be within the range of 0.01 to 5 mm, however, itwill be appreciated that the size and position of holes 10 will varywith module size, fibre packing density, fibre diameter, fibre pore sizeand other factors.

[0060] Another way to reduce maldistribution of gas/air is to use alayer of porous sheet (not shown) which has much smaller pore size thanthe holes 10. In this case, the major pressure drop of air will beacross the porous sheet. If the porous sheet has uniformly distributedpores, the air distribution across the air end of the module will tendto be evenly spread.

[0061] To further improve distribution of air bubbles, a porous tube 16can be inserted in the centre of the cylindrical module 4. When airpasses through porous tube 16, it produces uniform bubbles which passout through the array of fibres scouring solids on the fibre membranewalls. It will be appreciated that more than one porous tube could beused and such tubes could be distributed throughout the bundle. Fibresof large pore size or made of non-woven material could also be used asporous tubes within the bundle. FIG. 6 illustrates this form of module.

[0062] Referring to FIG. 7, air may be fed into a plenum chamber 17below the aeration holes 10 by an air supply tube running from above thefeed tank to the bottom of the membrane module. This tube may run downthe centre of the membrane module or down the outside. The plenumchamber 17 may also be connected to or form part of a lower manifold 18which may be used alternately for supply of aeration gas or as a liquidmanifold for removal of concentrated backwash liquid from the tankduring draindown or backwashing from the bottom of the module.

[0063]FIGS. 8A and 8B shows the trial results of the same module underdifferent conditions labeled by several zones. The water in the cylindertank was drained down every 10 cycles in zones 1 to 4. The dischargerate of concentrated liquid waste is thus calculated as 3.2% of the feedvolume. Zone 5 was run under the discharge of liquid waste every 3cycles at a rate of 10.2% of the feed.

[0064] Zones 1 and 2 compare the effect of using a porous sheet at theair end on the suction performance for the module with a screensurrounding the fibre bundle. Initially the suction pressure decreased(i.e. TMP increased) quickly because of the module was new. Then bothsuction pressure and resistance tended to be stable. By comparison, theincrease in suction resistance was faster after removing the poroussheet as illustrated in Zone 2. These results illustrate that the airend combined with a porous sheet helps to distribute air between fibres.

[0065] The use of the screen 8 has a dual effect on filtration. Therestriction of fibre movement by screen facilitates solid accumulationduring suction. On the other hand, limited free space between fibresreduces coalescence of air bubbles, producing better scouring effect. Ithas also been found that the restriction of fibre movement inconjunction with the movement of gas bubbles produces high frequencyvibrations in the fibres and rubbing between the closely packed fibresurfaces which further improves the removal of accumulated solids. Zones3 and 4 in FIGS. 8A and 8B represent results for the same modules withand without a screen.

[0066] During the operation in Zone 3 some by-pass of air bubbles wasobserved. This was due to different resistance around the aerationholes, especially on the border where comparatively less fibres weredistributed around those holes. We therefore used a porous annulus sheetcovering holes at the outer border of the lower potting head. Results inZone 4 show the improvement compared to Zone 3.

[0067] Solid concentration is an important issue to filtration andfouling rate. When a tank drain was carried out every 10 cycles, solidswere built up quickly, which influenced filtration performance. When thetank was drained down every 3 cycles, the increase in suction resistancewas significantly reduced as reflected in Zone 5.

[0068] The frequency of air scrubbing and backwash on the filtrationperformance was also investigated. FIG. 9 shows the resistance increasefor 30 minute suction and then backwash and air scrubbing. Compared withthe resistance increase in Zone 5 in FIG. 8, resistance increase wasfaster when suction time was longer between backwashes.

[0069] Longer term trials were conducted to compare the effect of poroussheet on suction performance. FIGS. 10 and 11 show the resistanceincrease for more than 6 days operation, with and without the poroussheet. For the module not connected to a porous sheet, suctionresistance increased slowly by ca. 20% during 8 days, while no obviousresistance increase during 6 days operation when a porous sheet was usedto improve air distribution. These results and the result shown in Zones1 and 2 in FIG. 8 suggest that a porous sheet helps uniform airdistribution.

[0070] FIGS. 12-14 are graphs which illustrate the effect of the bubblescouring on backwash efficiency. The scouring is conducted a regularintervals as shown the buildup of resistance followed by a sharp declineat the time of the scouring stage.

[0071]FIG. 12 shows the effect of not using a liquid backwash inconjunction with the gas scouring. At the beginning of the test a normalliquid backwash where filtrate is pumped back through the fibre lumensas a liquid backwash in conjunction with the gas scouring along theoutside of the fibres. The liquid backwash was then stopped and onlyregular gas scouring was used. It was found that even without the liquidbackwash a backwash efficiency of around 90% could be achieved.

[0072]FIG. 13 shows the effect of no gas scouring during the backwashphase. Again the initial part of the test used a normal liquid backwashwhere filtrate is pumped back through the fibre lumens as a liquidbackwash in conjunction with the gas scouring along the outside of thefibres. The gas scouring was then stopped between about 9:15 and 10:45.As shown on the graph the backwash efficiency dropped dramatically fromabout 96% using gas scouring to about 41% without gas scouring. Thereturn of gas scouring showed a marked improvement in backwashefficiency.

[0073]FIG. 14 illustrates the effect of scouring fully within the bundleas against scouring only the outer fibres. Again the beginning of thetest shows a normal backwash regime with liquid backwash and gasscouring up until around 9:00. The gas scouring was then limited to theoutside of the fibre bundle. The backwash efficiency again degradeddramatically from about 98% during normal operation to 58% with therestricted gas scouring.

[0074] The embodiments relate to membrane filtration systems andtypically to a system using suction to produce transmembrane pressure,however, it will be appreciated that the scouring system is equallyapplicable to any form of fibre membrane filtration process, includingpressurised filtration systems.

[0075] The scouring process and method may be used in conjunction withany standard backwashing regimes including liquid backwashing,pressurised gas backwashing, combinations of both, as well as withchemical cleaning and dosing arrangements.

[0076] The scouring process would normally be used in conjunction withthe backwash stage, however, it may also be used continually during thefiltration and backwash stages. Cleaning chemicals such as chlorine maybe added to the gas providing the bubbles to further assist the scouringprocess. Solids removed in the scouring process may be intermittently orcontinually removed. With continual removal of solid a clarifier or thelike can be used. The clarifier can be used in front of the module, inparallel with module or the module can be in the clarifier itself.Chemical dosing can be used in conjunction with the clarifier whenrequired.

[0077] The filter system using such a scouring process may be used forsewage/biological waste treatment or combined with a bioreactor,activated sludge or similar system.

[0078] It will be appreciated that further embodiments andexemplifications of the invention are possible without departing fromthe spirit or scope of the invention described.

What is claimed is:
 1. A method for filtering a feed liquid, the methodcomprising: providing a vessel; providing a membrane module, themembrane module comprising a plurality of porous hollow fiber membranes,the membranes comprising a plurality of pores and an outer surface,wherein the membranes are mounted in a header in close proximity to oneanother so as to prevent excessive movement therebetween, wherein themembranes form an array, wherein gas bubbles may be introduced into themembrane module, and wherein the membrane module is contained within thevessel; providing a feed liquid to the vessel, the feed liquidcomprising a fouling material, wherein the feed liquid is provided tothe vessel at a rate sufficient to cause an overflow; applying atransmembrane pressure to the membranes in the module, whereby afiltrate passes through pores in the membranes, thereby producing aconcentrated feed comprising the fouling material in the vessel; andremoving the fouling material from the vessel, wherein the foulingmaterial is carried out of the vessel in the overflow therefrom.
 2. Themethod according to claim 1, further comprising: connecting the headerto a source of a pressurized gas; and providing, through the header butnot through the pores of the membranes, gas bubbles in a uniformdistribution relative to the porous membrane array such that the gasbubbles move past the outer surfaces of the membranes and vibrate themembranes to dislodge the fouling material therefrom.
 3. The methodaccording to claim 1, further comprising: mounting the membranesrelative to one another so as to produce a rubbing effect between themembranes when vibrated.
 4. The method according to claim 3, wherein thehollow fiber membranes are arranged in at least one bundle.
 5. Themethod according to claim 4, wherein the bundle is surrounded by aperforated cage, whereby excessive movement between the hollow fibermembranes is prevented.
 6. The method according to claim 4, comprisingthe additional step of: providing gas bubbles from within the modulethrough gas distribution holes or openings in the header.
 7. The methodaccording to claim 1, further comprising: providing gas bubbles fromwithin the module through at least one tube situated within the module.8. The method according to claim 7, wherein the tube comprises aplurality of holes.
 9. The method according to claim 7, wherein the tubecomprises a comb of tubes.
 10. The method according to claim 1, furthercomprising: draining down a liquid within the vessel to removeaccumulated solids dislodged from the membranes.
 11. The methodaccording to claim 10, wherein the draining down comprises periodicallydraining down.
 12. The method according to claim 10, wherein thedraining down comprises continuously draining down.
 13. The methodaccording to claim 1, further comprising: scouring the membranes. 14.The method according to claim 13, wherein the step of scouring comprisesliquid backwashing.
 15. The method according to claim 13, wherein thestep of scouring comprises pressurized gas backwashing.
 16. The methodaccording to claim 13, wherein the step of scouring comprises chemicallycleaning.
 17. The method according to claim 13, wherein the step ofscouring comprises chemically dosing.
 18. The method according to claim13, wherein the scouring is continuous.
 19. The method according toclaim 13, wherein the scouring is intermittent.
 20. A filtration systemcomprising: a membrane module comprising a plurality of porous hollowmembrane fibers, each of the fibers having an upper end and a lower end,the fibers extending longitudinally between and mounted at the upper endto an upper potting head and at the lower end to a lower potting head,wherein the fibers are sealed at the lower end and open at the upper endto allow removal of a filtrate, the fibers being arranged in closeproximity to one another and mounted in a bundle in a substantially tautmanner between the upper potting head and the lower potting head toprevent excessive movement therebetween, wherein the fibers aresurrounded by a perforated cage to further prevent excessive movement ofthe fibers, the fibers being substantially uniformly mounted in thelower potting head relative to a distributed array of aeration holes inthe lower potting head, wherein the aeration holes are sized and locatedsuch that bubbles, formed by a pressurized gas passing therethrough whenthe module is immersed in a liquid, pass substantially uniformly betweenthe fibers, wherein the lower potting head is connected to a source ofthe pressurized gas, and wherein the fibers are arranged to be vibratedby the gas bubbles, the fibers being mounted relative to one another soas to produce a rubbing effect between the fibers when vibrated by thegas bubbles; and a vessel, wherein the membrane module is situated inthe vessel, the vessel comprising a feed inlet whereby a feed liquid isprovided to the vessel at a rate sufficient to cause an overflow, suchthat at least one fouling material is carried out of the vessel in theoverflow.
 21. The filtration system according to claim 20, furthercomprising a porous sheet through which a pressurized gas is supplied,whereby gas bubbles are provided from within the module.
 22. Thefiltration system according to claim 20, further comprising at least oneporous tube through which a pressurized gas is supplied, whereby gasbubbles are provided from within the module.
 23. The filtration systemaccording to claim 22, wherein the porous tube comprises a comb ofporous tubes.
 24. A method of removing accumulated solids from an outersurface of a plurality of porous hollow fiber membranes, the methodcomprising: providing a plurality of porous hollow fiber membranes, theporous hollow fiber membranes extending longitudinally in an array toform a membrane module, wherein the membranes are arranged in closeproximity to one another and mounted to prevent excessive movementtherebetween, wherein the module is contained within a vessel;providing, from within the array, by means other than gas passingthrough the pores of the membranes, uniformly distributed gas bubbles,the distribution being such that the bubbles pass substantiallyuniformly between each membrane in the array to scour the surface of themembranes, vibrate the membranes, and remove accumulated solids fromwithin the membrane module; and removing accumulated solids from thevessel, wherein the accumulated solids are carried out of the vessel inan overflow of a concentrated feed therefrom.
 25. The method accordingto claim 24, wherein the membranes are mounted vertically to form thearray and the bubbles pass generally parallel to a longitudinal extentof the fibers.
 26. The method according to claim 25, wherein theuniformly distributed gas bubbles are provided at a lower end of thearray.